1. Field of the Invention
The present invention relates generally to venetian blinds of the type having a plurality of parallel horizontal slats that may be set simultaneously at any of several angles so as to vary the amount of light admitted through the blind. More specifically, the invention pertains to a new and improved method and apparatus for assembling such blinds.
2. Discussion of the Prior Art
Venetian blinds have been in existence for over 200 years and generally include a horizontal support structure located at the top of the blind and attached to a support surface by support brackets. Suspended from the support structure are a multitude of parallel horizontal slats which commonly have a slight curvature in the transverse direction. The slats are held in place by two or more tape ladders suspended from the support structure. Each slat is supported by a separate rung of the tape ladder such that by shifting vertical runs of the tape ladders, the slats can be tilted by pivoting them about their longitudinal axes. A plurality of lift cords are disposed within corresponding holes punched through the slats. A knot is provided in the lift cord and disposed underneath the lowermost slat so that when the opposite end of the lift cord is pulled, the lowermost slat is lifted upward toward the support structure so as to collect each of the above slats in a stacked relationship. The position of the lift cord can be fixed by use of a brake disposed within the support structure. Thus, the position of the lowermost slat can be set.
Numerous examples of prior art devices for assembling and manufacturing such venetian blinds can be found in U.S. Pat. Nos. 3,281,914, 3,555,864, 3,824,657, 4,073,044, 4,790,226 and 4,730,372, in addition to Great Britain patent 713,802. Typically, these machines include a supply station, a forming station, an accumulator station, a punch/cut station and a lacing station. The supply station contains a continuous coil or roll of aluminum slat material. From the supply station, the slat material is fed into the forming station where a slight transverse curvature is applied to the slat material by mating rollers having convex and concave outer surfaces. After the slat material is formed, it is fed into an accumulator station where a predetermined length of slat material is maintained in reserve in a single loop so as to satisfy the demands of downstream drive wheels. The drive wheels are located at the entrance of the punch/cut station and serve to feed the slat material from the accumulator into the punch/cut station at predetermined intervals and at accelerated speeds. The punch/cut station includes a cutting substation and at least two punching substations. These substations cut the slat into predetermined lengths and punch holes through the slat into which the lift cords may be placed. At the exit of the punch/cut station is another drive wheel which, at predetermined intervals, feeds the cut and punched slat out of the punch/cut station and into the lacing station. The lacing station typically includes two or more lacing towers, each tower having a continuous supply of tape ladder material. Disposed in each lacing tower are a plurality of lifts and spring-loaded latches for supporting the cut slats after they have been inserted into the tape ladders and lifted to an elevated position. The cut slats are inserted into the tape ladders and the lifts are then used to lift the slats vertically past the latches so as to temporarily store the slats with previously processed slats. The tape ladder is woven slightly along the longitudinal axis of the slats by alternately moving the tape ladder back and forth as each new slat is fed into the tape ladder. As a result of this weaving, the cross rungs of the tape ladder are displaced from the vertical axis of the tape ladder so that a vertical opening is created along the vertical axis into which a lift cord for the blind may later be placed.
These prior art machines and methods for assembling venetian blinds have several limitations and problems. Most importantly, many of the machines must be operated at a relatively slow speed in order to accurately cut the blinds and reliably assemble them into the tape ladders without causing breakage of slats. One specific problem is accurately locating the slat material in the punch/cut station at a high rate of speed. When the drive wheels placing the slat material into the punch/cut station operate by accelerating and retarding at a relatively slow speed, there is little slippage between the drive wheels and the slat material. However, when the slat material is moved at a greater speed, the slippage between the wheels and the slat material becomes significant due to the inertia of the slat material during both starting and stopping.
A further problem with high speed operation involves the control of the cut slats upon being fed into the lacing station. At high speeds, the slats have a tendency to fly out of their intended path through the lacing station and become damaged as a result. In addition, prior art machines have typically included a fixed backstop to abruptly stop the movement of the slats once they reach the end of the lacing station so that they can be properly positioned for lacing and stacking. However, as the slats are fed into the lacing station at relatively higher speeds, they may be damaged, broken or rebound out of the desired position when they strike the fixed backstop.
Solutions have been developed to address some of these problems. To compensate for the slip in the drive wheels caused by high speed movement, a manual method for measuring and compensating for the slippage was developed and disclosed in previously mentioned U.S. Pat. No. 4,790,226. This method involves operating the assembly machine to first feed one slat all the way through the machine to the lacing station. The operator then manually measures the length of the first cut slat and if there is any error or deviation from the requested length, he/she manually inputs, via a keyboard on a control panel, the error percentage so that the computer associated with the assembly machine can compensate for this error with the remaining slats.
To address the flying slat problem, past machines have provided certain guide means which typically have included a pair of slanted deflector plates located above and below the intended path of the slat and located immediately adjacent to each of the lacing towers as disclosed in previously mentioned U.S. Pat. No. 4,730,372. However, to applicant's knowledge, no continuous guide has been provided in prior art systems which would be desirable to maintain control of the slats through the entire process. In order to address these problems, and others, and to achieve an improved method and apparatus for assembling blinds, the following invention has been developed.